How to store and retrieve S/MIME certificates in Open Directory (LDAP) of macOS Server?

Is it possible to use the Open Directory of the macOS Server app to store and retrieve S/MIME (X.509) certificates with the user data? *Background:* I would like to share our public S/MIME certificates over our LDAP, so they can automatically be retrieved from any (supporting) client without having to import them manually. I have found articles that claim it is possible in general with OpenLDAP, but how can it be done with Open Directory? I understand there are the attributes userCertificate and userSMIMECertificate for this. Are they available in Open Directory, and if not, can they be added? And once they are added, can they be updated through the Server app or just from the command line? The server is on Sierra in case that matters. I'd appreciate any reply or comment or link to a howto that could help.